Polymers have come to be used in various fields not only as a general purpose structure-forming material but also as a value-added type material having functions and performances of a high degree. This is followed by an increase in the importance of producing high molecular materials under precise design. Attentions are paid on silsesquioxane derivatives of a cage type having a dimethylsiloxy group as an organic-inorganic composite material containing silsesquioxane as an inorganic component. This is because they are expected to be applied to precursors of organic/inorganic hybrid materials, low dielectric materials, optical crystals and materials forming liquid crystal display elements, and the reason therefor resides in that the above silsesquioxane derivatives have a structure close to those of silica and zeolite. Cage type silsesquioxanes in which a hydroxyl group (J. Am. Chem. Soc., 122 (200), 6979-), an epoxy group (Chemistry of Materials, 8 (1996), 1592-) or a methacryloyloxy group (Macromolecules, 29 (1996), 2327-) is bonded to a dimethylsiloxy group are reported. So-called organic-inorganic composite materials of organic polymers and silsesquioxanes are prepared by making use of the above functional groups. The organic-inorganic composite materials can be obtained by radically polymerizing cage type silsesquioxanes having a methacryloyloxy group alone or under the coexistence of other acryl base monomers.
In order to optimize the functions of high molecular materials according to purposes, the molecular properties of a polymer and the properties thereof as a molecular aggregate have to be precisely analyzed, and this makes it necessary to use a polymer having a distinct structure. However, conventional organic-inorganic composite materials do not contain polymers in which a structure is controlled as an organic component including the composite materials described above. A large part of them is obtained by mechanically blending silsesquioxanes with organic polymers, and therefore it used to be very difficult to control a structure thereof as a molecular aggregate of a composite matter. Then, it has come to be tried to control a structure of a polymer by using a polymerization initiator. It is disclosed in Chem. Rev., 101 (2001), 2921- that an α-haloester group is a good polymerization initiator for styrene base monomers and methacrylic acid base monomers in living polymerization, but silsesquioxane derivatives having an α-haloester group have not been known to date.